Chris, I had a similar problem with a hoop house that I bought on Ebay, when the entire covering deteriorated after one summer. I think it took me 3 years to figure out a plan to add some wooden framing to the steel tubing without having to do a lot of notching, drilling, etc. -- but I finally did it and it has worked out great!
the original hoop house:
after we added some wood and a new covering:
all of the wood is 1x4 treated lumber. The lengthwise horizontal pieces are attached to the metal tubing with pipe clamps. The end framework is basically freestanding, except for being attached at the top with a bracket and attached to the "baseboard" with screws. We made the doors with 1x2's - but in retrospect I think I would use 1x4's for them; or, if your hoop house is large enough, use inexpensive wooden screen doors and cover the screen with plastic (that's what I'm doing with my new, larger greenhouse that we started building last fall and still need to cover).
We used lath strips and screws to fasten the plastic covering to the wooden framing.
I'll take some "detail" photographs of it tomorrow for you ... I'm happy to share this because I'm so happy with the way it worked out; we built the framing in 2014, so I'm going on the 3rd year. This year we'll be covering both the new greenhouse and this smaller hoop house with actual greenhouse plastic (6 mil, UV protected, life expectancy at least 4 years) as opposed to the cheap 3 mil plastic film that I originally used to recover the HH.
