We have a local powder coater, but it seems very expensive. Spray cans will do it just fine.
I obtained actual ground ball bearings with seals to replace the open junk "bearings" those harbor freight wheels originally came with. Finished installing them last night. Turned out great. I put in a grease zirk in the sidewall of the hub, picked off the inner seal of each bearing before pressing in, lathe-cut an inner race preload spacer to drop inbetween the two bearings. Now they work SWEET! Then, mounting them onto the deck, I added supports to both sides of each fixed wheel at the back of the deck, instead of support from one side. And more custom spacers so only the inner races contact the mounting surfaces. Looks like it will last now. I made a couple other changes as well. I added a swivel to the hitch, full 360 degrees, right up next to the tractor end, so the mower could swivel compared to the tractor (like the tractor could be on level ground next to a bank and the mower could be on the bank sidehill itself, and any angle without bending anything). I added a couple more mounting positions to the hitch, so it can overlap 3 inches to a 60 inch belly mower, or 2 inches to a 40 inch belly mower. And I made the clutch lever a bit smaller as it was hitting the one tire. Installed the grease zirks in the caster pivots, and added holes for cotter pins here too. And added 1" square tube gussets across each of the two 22.5 degree angles in the hitch tube.
Saturday is the big test, my wife will mow the yard and orchard with it and give me feedback (or break it). I will be watching and photographing. Then I will load it onto the trailer and take it to mow my 1.5 acre airstrip behind my little TSC Husky 38" rider, which usually takes 1.25 hours. If all goes well, I will then build belt gaurds, a permanent throttle lever mount, and add a kill switch extension to the tractor, before dissassembly for paint.