If your bearings are properly adjusted they will last a long time and without heat issues. Bearings get hot when they are too tight. Sounds like you rely on other people to maintain your trailer. About time you get your hands dirty and DIY.
I will tighten the castle nut with a wrench to ensure the bearings are seated then back off the nut. I will next hand tighten the nut then back it off just enuf to install the cotter pin. There is a very slight amount of play in my bearings when I do it this way but it works for me and there is no heat buildup as a result. I've pulled this trailer all over the country for the past five years and my wheels are always cool or slightly warm to the touch depending on brake use. BTW, I've only repacked the bearings once and I don't shoot grease into the axle.