No allen key hole and I've tried the spin off method and now I think I cracked the pipe inside the spout. I believe we have mainly pex tubing as piping in this place so I was wondering if there is another way that the manufacturer could've installed this tub spout.

There are only two types. Slip on, (they're chrome covered plastic and screw on which are mostly chrome over brass. Since trailer manufactures like to hold the cost down they go with plastic. I don't know how a spout connects back tp Pex. Perhaps one of the other experts can chime in. Good luck, Tom