* First I would address one thing at a time and take the boat off and put it on some wooden horses (upside-down). I would cover it with a tarp. This will help keep the inside completely dry when you are ready to paint it.
** Second, you need to completely over-haul your trailer
(fairly inexpensive). This is an area many overlook and it could be disastrous if something goes wrong.
-check the coupler for wear/damage. Does the cam lever come down easy on the ball? You can get a new kit at Northern Tool for a few dollars.
-are the tires/rims in good shape? These will cost about $50-75 each at Northern if they are dry-rotted. It looks like yours are in decent shape from the pictures. I would lift the trailer up and set the axle on some wooden blocks (do this in your permanent work area). Take both the tires of and clean them thoroughly. I would use a grinder to take care of the rust spots; spend some time on this and you can get rid of all the rust. Use duct tape to protect the tires and you can use it for paint masking later. Once you have it cleaned up; I would take a small paint brush and dip it in primer - use it to fill the old rust divots by blotting with a brush. Once you have built up the divots. Lightly sand so that it is flush with the old paint and put on a few coats of primer. After that; apply a couple coats of paint. Try not to rush your coats; let them set and build up and good protective coat. I neat trick to do after this process is to brush the rim with a light coat of fiberglass resin; it is tricky to not have runs and to get the catalyst mix right as to not kick too fast. After that; you can do another light sand and paint again...It should last until the next ice-age with minimal rust...
-completely rebuild your hubs on each wheel (~$20 total). Take out your old bearings and knock out the old races in the bugs and replace. I would clean the heck out of the old hub with a cheap wire brush and spray it with some primer to thwart future rust. Bearings+races cost around $10 at Northern-check your axle diameter. I would get bearing budding grease caps so you can keep your bearings greased (~$10) and some plastic bearing caps. I usually grease my bearings about 2-3 times a year based on about 75-100 boat trips (20 miles round trip).
-replace your bunks with some light weight wood - pine, etc. Take a sander and sand the ends smooth and any rough areas. Then, take a smaller roller and apply about 2-3 coats of resin to your boards. Let this dry. Set up your boards and mark your bolt holes in your boards. Then drill holes about 1/4" larger than your bolts in your boards. Counter sink your holes on both sides of the board about 3/8" to thwart the fiberglass from cracking when you install. Then put some resin down these holes; do not seal them up; just coat the sides. Buy some heavy-weight outdoor carpet at Lowes; get some stainless steal staples, glue gun-glue sticks. Apply your carpet with the staple gun and use the glue-gun to clean up any flaps or to help you keep things aligned. Locate your holes and cut a plus+ figure to attach to your trailer braces. Use galvanized bolts and make sure they are not sticking up as to rub your boat hull. You can add some silicon caulk in to the hole to protect from rot if you want to be even more through. You may want to add some sliders (plastic) pieces to your bunks if you find it difficult to get your boat off the trailer where you are launching. You can buy different densities of plastic at hardware stores over in the cut glass section. You can melt/bend/cut it very easy and it is fairly cheap. Just be cognitive of the new slickness when launching/trailering the boat.
-I would replace all the trailer wiring with LED if it is suspect while you have everything apart(~$50) for kit. Also weld or mount a piece of angle iron to protect each taillight from backing in to something. You can get this for a few dollars at most hardware stores. Paint it up; drill some holes and mount. You want to protect those lights. I ended up adding some cheap running lights as signal lights on my high boards. I just wired them in to the signal wire. You can use them as break lights or signal; just not both unless you add some kind of voltage relay; then-it would be cheaper to buy a combination brake, taillight, signal light. Use heat shrink tube for all your connections and I use a hot glue gun to firm up my connections for extra protection. Also, for mounting my wiring in some spots.
-Sand trailer very well; prime, paint, add pin-striping (~$2-3), add side reflectors (~$2)
for exact placement of lights/reflectors/etc.
Hope this helps...Boat stuff is more involved and I will send Part 1 a bit later...