Rusty Rear Brake Lines

Hello- helping a friend with a 2009 Tacoma- flunked inspection here in Vermont due to rust on the rear brake lines. I replaced all the lines on my Rav4 with cunifer I flared myself with a Rigid flare tool- worked great. Also did all the lines on a rustbucket Mercedes.
The rear lines on this Tacoma that need replacing are the two long runs- rust at both junction ends, so "patching" doesn't really make sense, and the front junction clamp with the 90 degree fittings also is rusty/needs replacement ($26 part at dealer- not too bad).
My question: two of the support clamps along these runs are inaccessible (I think?) unless the fuel tank is dropped or the bed removed- is this true? And if so, which is the lesser of two evils?
I would clean the bed bolts from below (if I can access them) with a thread cleaner (similar to a dye, but made specifically for cleaning threads, not "cutting" them) before trying to loosen them as well as soaking in ATF fluid/acetone or PB Blaster from both above and below for a day or two before trying to loosen them.
Does heat (propane torch) work here or will plastic be melted?
Dealer wants $750 for replacing these two lines! (I can make custom lines plus buy union clamp from dealer for $75)

In summary, does either the fuel tank or the bed have to be moved to replace these rear lines? (I don't like fishing new line past clamps engineers deemed to be necessary, but is that being overly cautious?)
If either the tank is dropped or the bed moved, can we use the full factory lines or do we have to custom make lines?
Which is easier, moving the bed or dropping the tank?
Thanks in advance for any advice, other than moving South. (While not a bad idea, we're skiers!)

 

You can access them from underneath. Might help to drop space tire