Only the one brace as far as I know, at the dinette end. But don't know for sure. Look for rivet holes at the end of the cabinets. That is where it attaches. Sides of lower cabinet to bottom of upper.
IMO it would be easier to just order the snap cap kit from Scamp
for a 16 ft. Tip: Call and order over the phone, ask if they will ship US Postal. Shipping through the web site store with FedEx or UPS is super high. Also get some butyl tape, I think a tiny bit of that under the snap cap washer helps it seal.
The seam tape from scamp is "ok" but I had to use 3M spray adhesive in order for it to stick. That worked and was pretty easy. Just spray a quick line of adhesive along the seam, let it tack for a few minutes and put tape on over the adhesive. I found that going around window seams the curve did not work out so well. Stress of curving the tape made it keep coming off. Full job I think you will want two rolls, but I think all of the walls can be done with one. Windows
will put you into the second roll.
Axle does not so much fail as it does just slowly allows the trailer to sit lower and lower. Like worn out leaf springs. Rubber inside axle provides torsion to the arm with the wheel on it. Rubber wears out over time and the trailer just rides lower. Yours does NOT appear to be riding low, maybe it was stored on stands as a hunting camp taking the weight
off of the rubber?
Having replaced mine I suggest getting the 5 on 4 bolt pattern and doing an adapter bracket for the spare. Allows for larger tires
(run cooler) and 5 on 4 hubs with brakes
are common the 4 bolt brake parts are harder to find in stock. I went with 4 bolt to avoid replacing wheels but would not if I had to do it again.
I have some before and after pictures someplace. Wheel well came across the rim between spindle and rubber of tire with old axle. New axle (2200 lb for a 13 ft.) and the wheel wells sits right where yours does, about middle of the rubber above the rim. And the original down angle was used to determine height new axle should provide.
Keep the pictures coming, we all love to see people bring these old trailers back with some love and sweat.