Well, this subject turned into a rabbit hole...

Here's a video from Devcon that shows using Flexane 80 to cast a roller wheel (at 2:13 in the video), so it would appear the stuff is fairly sturdy when cured. (Recommend sound off; there's no speaking and the soundtrack is painful.) From a cursory search, it looks like Flexane would cost $80-100 per tire.




Finally, a YouTube channel called Project Farm tested a number of roll-on bed liner products. If you watch the video closely, you can see that many of the liners cure to a hard finish and flake when damaged, while two of them (Herculiner and Durabak) seem to stay flexible. Herculiner runs ~$20/qt and Duraback ~$50/qt (Amazon prices).