I usually wait till late may for my Vet visit. I'll give the WNV and 5 way shots in April myself so the vaccines start building resistance before the mosquitos show up in late May. I wait till May for the Coggins, because I want it to be effective in October when I go hunting. I frequently have to cut the corner of Wyoming and they only accepts 6 months on the Coggins.
Since I have to go to the vet for the Coggins, Any teeth floating waits for that visit. And I usually only get their teeth floated every other year. My vet charges $40 for the coggins, But any health certificates I need the rest of the summer are included. Back Country Horsemen has a Shot/Coggins clinic that is cheaper, But then I'd have to pay for every health Certificate all summer as I travel.
My normal vet's office is only 1 mile away at most and I'd like to see him stay in business, so it's worth paying a little more to have him close and save me chasing monthly health certificates from a vet 20 miles away. I always just load the horses up and go to his office vs paying for a farm call. He has the stocks and everything to make working on the horses a breeze. Load the horses in the horse rack, give them the Tranq shot. Hook their halter up to the rack so it holds their head up at the right height, insert the Speculum and he has all the electronic and air driven files to do the work with hanging on his too board.
As far as the trailer, I do a good cleaning each April and October. The city turns on our secondary water April 15th and turn it off Oct 15th. It has so much more pressure than my house water, That I use it to really clean out the inside of the trailer in April after the winter and again in October and as needed during the summer. I have multiple car washes close by that I can spray off the outside as needed. I usually sort out the Dressing room and tack room April and Oct, Putting in or removing the extra stuff I need for the summer or winter months. Better sleeping bags, pannier for packing, hunting gear in the fall, lighter sleeping bags, and summer camping stuff in the spring.