I think I have it figured out now. I needed basic frame strength (cubes) plus top support (arches with a ridgepole) for shedding rain and snow. And a sturdy cover.
Got them all figured out now!
The canopy is designed to be separate from the boat. I park the boat and just pull the canopy over it. No trying to back it into a small shelter in the dark. Making the canopy as small and unintrusive as possible.
The base is made of 1.25" PVC pipe. The bottom of the base is like a sled; only a crosspiece at the back bottom. Above the boat, there are crosspieces for rigidity and strength. Those crosspieces above the boat are 6" higher than the highest part of the boat for safe clearance.
The top of the canopy frame is made from .5" PVC pipe and fittings so it can be bent into an arch. Arches are strong and so can be made from easily bendable smaller PVC pipe. And I have an idea that will help support the tarp cover that I will mention later.
Dimensions of this canopy vary by boat. I need 5' high crosspieces at the top of the base to clear my 54" pedestal seats above ground. As they say, "Your requirements may vary".
Mine will be 20' long and 7' wide and about 7' tall. The 20' length will protect the boat and trailer (the trailer spare tire, winch, and hitch will last longer when sheltered). Adjust yours as needed. It's the fittings that are the tricky part unless you don't care if the structure is 10" tall!
And finding the fittings is the hardest part. I've spent weeks searching local and internet sources for all the right fittings. Rule #1: No one offers them all! So this design is one that offers one internet source for "odd fittings" and the rest really are locally available. Indeed, the design was forced by what I could get locally and from only one internet source.
The base is made of 2 parallel pipes with one cross piece at the back. This is because the whole structure is designed to be pulled over the boat and trailer wherever it is parked. The uprights from the bottom pipes and the crosspieces above the boat will make it a rigid structure.
At the point above the boat, the structure changes from 1.25" PVC pipe to .5" PVC pipe. And that's where it changes from squares to arches.
The tops of the base have 45 degree elbows (with a reducing bushing) in them. The top of the arch will have .5" cross pieces aligned as a ridgepole. From each crosspiece there will be a half arch .5" pipe into the reducing bushing.
The frame top will be covered with plastic snow fence for support of the tarp cover (and I am ordering a 12' x 20" heavy duty UV resistant tarp for only $42). The snow fence and tarp will be firmly attached to the PVC frame, not the trailer, so no boat attachments will be required. I will, however, put an eyebolt through the PVC frame on each side to attach it to the boat with a bungee cord. The boat is simply an anchor in this case. That way, it can't be blown off by wind.
My material list (letters relate to the above diagram):
A. .5" Cross - 3 each
B. 1.25" Tee - 6 each
C. 1.25" 5 Way - 6 each
D. 1.25" 3 Way - 2 each
E. Caps (not needed) - Forget that one unless you can't find some parts and need a cap for a part with an extra outlet)
F. .5" Tee - 2 each
G. 1.25" 90 degree Elbow - 2 each
H. 1.25" 4 Way - 4 each
C and H also require a 45 degree Elbow and a 1.25" to .5" Bushing - 10 each
And I think I need thirteen 10' 1.25" PVC pipes and six 10' .5" PVC pipes.
If anyone detects an error in design, please let me know ASAP!
I've bought all the fittings I can locally and ordered the other parts online (Creative Shelters). When everything arrives, I'll figure out what order to assemble the parts in, and report on that later.
I will, of course, take many pictures during construction! You can't believe how relieved I am to have finally solved the design issues. It was quite a challenge, as PVC fittings are limited in both design and availability! I could have easily done it with a 45 degree roof, but that was just too tall. I had a vision of a better way and I found it! The design aspect was half the "fun"... You wouldn't believe how many sheets of graph paper I used just getting THIS far. LOL!
When it is completed, I will probably rewrite the whole post for better clarity and add pictures, but this is the best I can do until I've actually built the thing.