Made more progress with fixing up my trailer. After completing the rear and side ramps, I built up removable sides and a divider (so smaller equipment can stay up front, accessible via the side ramp, while larger equipment uses the rear ramps). The existing floorboards were pretty old/rotten, with a bunch of smaller pieces used to cheaply fix the worst areas, so I bought a bunch of 18' 2x10s, cut them to the right length (just under 18'), painted them with Behr Extra Textured Deckover paint (as smooth painted wood can get very slippery in winter), removed the existing deck, and began installing the new boards today:
Painting the boards:
I painted them ahead of time, as the trailer is in active use, and the paint needs several days of drying time, with the temp between 10-30C, they've been sitting in my smaller attached garage with the heater on waiting for a bit of downtime to do the install.
Removed the existing boards, cut off and ground the old screws/bolt remnants off/flat:
Most of the boards installed:
There's 11" left to fill. I was thinking of cutting the 2 remaining 2x10's in 5.5" strips, but now I'm thinking that, to maximize strength for the occasional time when I haul a vehicle with this trailer (it's rated for 12K lbs), it might be better to install a full width 2x10 on the outside, then put in a 2" stripe in the remaining space. For regular use, it doesn't make a difference, as lawnmowers/snowblowers/plows are relatively light (none of the equipment I have is over 1000 lbs, but I'm considering getting some slightly bigger stuff getting up to 2K lbs).
I'm using 2" self-threading Robertson trailer screws (6 per board, a pair at each end and in the middle), and need to pre-drill 7/32" holes for them, which has gone alright (haven't missed hitting the metal crossmember the screw needs to go into yet). And I was going to ask for suggestions on how to deal with a couple screws that didn't go in all the way (one the robertson bit broke off in the screw head, the other the screw head decided it preferred being round instead of square), but as I was about to type it, I remembered the head was just a little bit above the surface of the wood, enough to get the end of visegrips on the head and then screw it out to put a new screw in it's place (and I just went out and removed both screws).
Oh yeah, Home Depot sucks for buying impact bits for driving these screws in, as, in an effort to get you to part with more money than you want to, spreads out where these bits are all over their store, some are with the impact drills, some are in separate, standalone displays near cash registers or as end-caps, some are in with the screws.