Question Using "Bondo Hair" to patch a hole. Or just Bondo Body Filler alone.

[JeffAndPam]

Ok, time to post this one here (a continuation of this sub-question here)
So I have this hole in the side of my RV:

I should have placed a ruler by it, but the main hole is about 3 inches high. The hole is indented I'd say a 1/4 in.
For those curious: Basically I was parked VERY close to the roof of our house, this section was behind the rear wheel of the RV. When pulling away from the house, I learned the hard way what "Tail swing" means. Oh, and the patch the roof will be later posted on some other forum.

Some Context on this repair:

1. I just want to cover it, doesn't have to be fancy. It's on an 18 year old RV that already has it's flaws. (In fact for spray paint, I'll just find the closet match at the hardware store).
2. The hole is about 10 feet off the ground. No one's going to touch it. It doesn't have to be structurally solid.
3. I also have other project to get to.

I've already got some good tips already. In addition, in my research on patching I came across this video were Evercoat Kitty Hair is used:

That looked somewhat easy. But a bit costly product.

I also found this product: Bondo Hair
I don't see it mentioned much, but this might fit my needs. Especially considering my context.

QUESTION: Does anyone see a downside of using this product for my particular project instead of the resin & cloth approach to fill the hole (then use Body Filler on that)?

OR BETTER YET, given that I don't need it to be structurally sound, is there any reason I can't use just the following:
Bondo Body Filler
for the whole job? That would cut down on cost (I have to buy that anyway) and simplify my fix....and let me got on to the other projects.

 

[Rich W.]

I used tiger hair bondo on a gouge in a fiberglass 5th wheel and I just saw it four or five years after the repair and it still looks good. Just do multiple thin layers and slowly build it up and it probably won't crack. Finish with Evercoat polyester glazing putty and high solids primer and then guide coat for final sanding for a nice smooth finish.

 

[Underboss]

On that big of a hole I would use the mat, start with small pieces and each layer gets progressively bigger. Fiberglass reinforced bondo has its place but not for that. If it was a small crack you could slightly widen it and used that bondo.

 

[Rich W.]

On that big of a hole I would use the mat, start with small pieces and each layer gets progressively bigger. Fiberglass reinforced bondo has its place but not for that. If it was a small crack you could slightly widen it and used that bondo.

agree - looking at that pic, it needs something structural in it as it is built up.

 

[JeffAndPam]

agree - looking at that pic, it needs something structural in it as it is built up.

So here's a question (I understand I'm new to this). I've seen the need for adding structural support when there's nothing behind the outer surface (and at times when there is).
In this case there is styrofoam directly behind it. I tried pushing on the center of the hole and it doesn't budge.
As I mentioned above, this is 10 feet high and won't ever be touched. Given that, will Bondo Body Filler work ok for me?

Understand this question is coming from someone who also has other things to work on (and spend money on).
I guess I'm looking for that "What bad thing will happen if I only use Bondo Body Filler to fill this hole?" answer.

 

[LMHS]

Pure bondo will crack. I have a spot on my bus that proves that. I did not make the repair. I was always told to build up the "hair" in multiple thin coats until the "dent" is filled. Make sure to allow plenty of time for each layer to dry (cure) completely, otherwise you seal uncured bondo and it will never dry, leading to cracks.

 

[Underboss]

So here's a question (I understand I'm new to this). I've seen the need for adding structural support when there's nothing behind the outer surface (and at times when there is).
In this case there is styrofoam directly behind it. I tried pushing on the center of the hole and it doesn't budge.
As I mentioned above, this is 10 feet high and won't ever be touched. Given that, will Bondo Body Filler work ok for me?

Understand this question is coming from someone who also has other things to work on (and spend money on).
I guess I'm looking for that "What bad thing will happen if I only use Bondo Body Filler to fill this hole?" answer.

You have asked and we have said what to do. You should either do it the right way or just leave it alone. But sticking a blob of bondo in there will not help. It will just crack. To put it in the simplest terms, bondo is not a hole filler, its a topping

 

[JeffAndPam]

Pure bondo will crack.

Ok, that makes sense.

Speaking of cracking, originally we thought our RV was off-white. When I went to look at one of the metal panels over the furnace, I saw the paint on it was white. So I thought the RV just needed a good washing (previous owner never washed it). But looking closer at the side of the RV, we can see a network of tiny cracks (developed after 18+ yrs). From a distance it looks off-white.

So I went to the store and found the lightest off-white I could find. It's gonna have to do.

 

[Underboss]

Ok, that makes sense.

Speaking of cracking, originally we thought our RV was off-white. When I went to look at one of the metal panels over the furnace, I saw the paint on it was white. So I thought the RV just needed a good washing (previous owner never washed it). But looking closer at the side of the RV, we can see a network of tiny cracks (developed after 18+ yrs). From a distance it looks off-white.

So I went to the store and found the lightest off-white I could find. It's gonna have to do.

It was probably not painted but clear coat over the gel coat

 

[GypsyR]

Bondo isn't structural. I would personally soak and put some fiber mat in there and fill the rest with fiberglass gel. Bondo is for leveling and fine finishing and you kind of need both. Fiberglass never sands out quite smooth enough. For me anyway. If you do a pretty good job of laying in and sanding down the fiberglass then a minimal amount of Bondo will be needed. You can buy small tubes of Bondo and catalyst for just such situations so nood for a big quart can of it.
Pretty sure this is a repeat of what I've said elsewhere, but anyway...