I don't have pictures, but this should help:
Electric Tongue Jack: Very easy. Just follow the directions. (You'll need some way to support the tongue of the trailer during the install. I just hooked it up to the car.)
Under frame tire carrier: I used the one linked below. Just followed the directions for install. The only part of the frame that had a wide enough gap to fit a tire in was just forward of the axle. It's very important to line up the two sides to the same point on the frame so that it doesn't bind when being pulled out/pushed in.
https://www.amazon.com/gp/product/B00KPRBBRO
There are a bunch of different styles for different types of frames. The one linked here is the one I got.
Others have mounted the spare under the tongue by making their own ... That would cost less. I also thought about mounting it to the underside of the bumper, but was worried it would hit when going over curbs and decided I didn't want the weight aft of the axle anyway.
Power cord holder: I just used the original parts plus some small pieces of scrap wood. The original was stapled together and then stapled to the underside of the bunk support. The staples didn't hold. I put it back together using screws and remounted it using screws.
Bumper: I installed these:
https://smile.amazon.com/dp/B071JM3GJD
I wasn't sure that would be sufficient so also had angle iron welded to the frame and bumper (run along the bottom of the frame to the bottom of the bumper). The bike rack mounts at four points along the bumper (two for each half) and I put one of those right next to where the frame meets the bumper so that it would be very close to the reinforcement. I used this sort of bike rack, which isn't perfect but does the job:
https://www.discountramps.com/bicycl...-bikes/p/BC4BM
I use lots of bungees to secure the bikes. They do rub against the bike rack though ... This could be better.
If you do a bike rack on the bumper, for safety you need to do two additional things: Know the fully-loaded weight of your trailer. You can get this at a CAT Scale. (To get the full trailer weight, you have to unhitch it while the measurement is taken so all of the trailer weight is on the scale.) You also need to know the tongue weight. You can get this using a tongue scale:
https://smile.amazon.com/gp/product/B007REJTGI
12-14% of the total trailer weight should be on the tongue. By adding bikes to the rear, you're removing weight from the tongue. If the tongue weight is too low the trailer can become very unstable at high speed and cause an accident.
For me, I ended up being okay on tongue weight. My solar panels and spare tire carrier are mounted forward of the axle and that offset the bike weight nicely. (In fact, I'm better off with the bikes than without. My tongue is too heavy without them.)
Solar panels: How you do this depends on what you want. e.g. wattage, type of panels, etc ... Lots of variation here. (There are books on this subject that go into wire sizes, run lengths, types of charge controllers, etc ...) My setup is pretty extreme and designed for extended stays in remote locations without using a generator. In summer, it'll run everything indefinitely. It will last through three consecutive rainy days. (The batteries are dead after the third one though. I need sun at least every fourth day.) I ran the wires down through the AC roof vent, then through the cabinets over the dinette, over to the wall between the dinette booth and bunks, and down inside the wall, to the dinette booth. I mounted the charge controller in the wall. The batteries just sit under the dinette booth and are kept from sliding around by a couple pieces of tall angle iron screwed into the floor.
Should you decide to do this: Be very careful to screw the panel mounts into the roof trusses. The roof between the trusses is very weak.
Sealing: This is how I did it: Figure out where you're going to screw the panels in, clean that part of the roof thoroughly, and mark the spots. Put self-leveling sealant on the roof where the mounts will sit. Put the panel onto the roof with the mounts at the locations marked. The self-leveling sealant will seal around the mounts and keep water from coming in from underneath the mounts. Drill pilot holes and screw the mounts down. Put more self-leveling sealant over the screws and mounts, completely covering the mount that's against the roof and the screw, and around the back side of the mount too. This will keep water from coming in along the screw or mount. It's very very important to seal the roof penetration properly and fully.
Should you decide to do something like replace the axle, unless this is the sort of thing you do on weekend for fun already have someone else do it. Really. It's all of 6 bolts for the springs and two wires for the brakes, but OH MY was that hard. All of the other stuff above I'd be comfortable doing again on a future trailer, but not that.