Used to use pads as well but now I rarely ride on gravel so he is pretty good with just shoes if I stick to the nearby trails which are soft.
If you only ride on yielding footing, that will alleviate some of the peripheral loading of conventional rims, but padding feed isn't just about protection but support, so if you ride on hard/flat surfaces, the hooves aren't solely(pardon pun) loaded on the walls, which will exacerbate weak connections & allow the foot to 'sink'.
We have tried wedge shoes with him, to bring the heel up, but once the shoes are off he goes back to his normal under run heels. .... I am hoping if I can keep his sole ( and of course everything underneath!) tougher he will not get so footsore
Underrun heels are too long but crushed forward, so wedging them isn't going to help, only potentially put even more pressure on them. They need *relieving* in order to relax back & down. If the horse has negative P3 angles due to the crushed heels, using a wedge pad under the frog *not the walls* can help though.
If the horse has such thin soles/such little protected internal structures, I wouldn't be leaving it unprotected on hard//rough ground. Painting soles with stuff to make them harder is going to provide minimal if any actual further protection. You might want to look into the new Easyshoe from Easycare as a winter answer. Being flexible, wide & with frog support, it's quite different in effect from rims.