I second getting horse hobble trained. You don’t have to be rough with him to do it. He is just learning another form of “submission” in accepting kindly restraint to your requests. He will be a BETTER horse for this added knowledge and it could come in handy should he ever get tangled in something!
The other option is covering the wheels and fender with a large piece of plywood tied on somehow, so he can’t paw them or get caught/cut on fender edge. Have seen this happen a couple times.
I consider relentless pawing while tied to be a bad habit. He could hurt himself and damage the trailer, flatten your tires! So horse then is taught to hobble while tied. No one gets hurt, horse gains knowledge, PATIENCE, and I am happier! Sometimes trailer is the only place we can tie to, he needs to tie and stand WELL for us.
I use burlap hobbles, not the strap with buckle types. Strap types are harder to get on and off fast, not wide enough for our big, broad- chested horses. Burlap hobbles easily adjust to size of horse, have never left a mark, can be cut fast if horse gets in trouble and are home made cheap.