I have the same issue on my Trillium
. I sprayed 3 coats of rocker panel (for vehicles) stuff on it before a long trip on many gravel roads. Maybe it helped a bit, but, in the end, I had one corner where the rocks punched right through the fiberglass.
Since then I've been on the hunt for something more permanent as I like to do a lot of back road travel. Looked at rubber/foam chip mats, but they ended up being too heavy and attachment involved contact cement. Then looked at diamond plate - which would have to be custom made to wrap around the corners, so too many $$$.
Then researched the truck bed liners. After looking at recommendations from many folks on truck forums about the good and bad, I found one, called Monstaliner. (Magnet Paints Manufacturers High Performance Specialty Coatings
). I emailed them requesting samples which they sent for free in the colours requested. Also watched quite a few youtube installation videos from them and others. It's a do-it-yourself material that is rolled onto a clean surface. For one gallon of tintable bedliner that includes 2 rollers, paint
brush, scuff pad and drill mixer, the cost is $145.40 US
Then you need to purchase the colour pigment concentrate in the colour of your choice. 1 gallon needs one 8 oz. can of Monstashade - the darker the colour the more expensive. Eg. Desert Sand $18.50 US.
The samples that arrived showed the thickness of the material and I was impressed. Due to the 30% difference in the US/CDN dollar, I'm waiting until the exchange rate is more friendly. Monstaliner has me convinced that it's the best, easiest, long-lasting do-it-yourself material. Also has UV protection.
Good luck in your search. Please share your results!