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It is about time! I am looking forward to pictures. Im also itching to see how you do your electrical.
Sorry to hear about the lumber. It is funny how you had problems with the wood that I didn't have problems, and vise versa. Here I am suggesting to use 2 x 6s because of how true they are. Guess it kind of depends on where you live.
One word of caution (hopefully that you already know or read prior to starting). The outer measurements of the rims for a 75 / 90 in most cases is 48 3/8 by 18 3/8.
Can't wait to see the pics!