The only thought I'd have on a permanent mount would be that I keep a 2x4 in my garage just for the purpose of perfectly lining up the PTO generator (on its little trailer) when I hook it up and get it running. Normally I find that it vibrates a bit, and it I carefully slip the 2x4 under the trailer and shift if an inch or so either way, it smoothes right out. With a permanent installation, you might have to keep moving the tractor by an inch or so before you got it perfect.
Of course I don't know if it's important to reduce this vibration, but seemed like a good idea to me.
I like having mine on a little trailer.. can take it to a neighbor's, out in the field, etc...
Just my thoughts...
Bob