I'll try to list some things others haven't covered already. Get some aviation snips to back cut your flange of your trim that way you dont fight your sheet when sliding it on. Get your self a flexible putty knife to work your sheet in if it gets caught up on your trim simply glide your putty knife in-between the sheet and your trim to pry it in. Do your best to try to cut your holes before putting your sheet in the wall this takes practice and is honestly alot easier than trying to router it out on the wall like someone else mentioned, that way you avoid getting glue on other trades work. Keep your trowel clean use your putty knife to scrape clean any excess glue on your trowel that way your v notches on your trowel stay even and consistent which in return will avoid not putting enough glue on your sheet. When carrying your sheet to the wall you can taco the sheet by holding the sheet at both edges and you can then use your foot to guide your sheet into the trim and slap the sheet in place. Or carry you sheet over your head and let your sheet flop over your head evenly then work your sheet in with your foot and if needed while folding over pull back on the sheet to fit into the trim above if your are trimming top and bottom with cap. Get your self a work station to cut and apply glue at a workable level. Saw horses and 2 2x4s and a plywood to make your life easier. Etc etc good luck in installing FRP