If you have the 5" extensions you are in good shape, you will have to do some tub heating, but only above the tires.
I used the heat gun on high, picked a warm day, and had the machine in the sun, heated it up for about 5-10 minutes above each wheel, and then used a 1"x8" board to start, then as I got more clearance, went with a 2"x4" eventually. You will have to repeat the process to get the desired clearance. Don't stop when you have just enough as the body will sag eventually, I'd say stop when you have about 2" clearance above the tires. The process will need to be repeated about once a year to maintain the clearance.
I think that your theory of using 20" tires is very valid, there's not much that the extra inch gains you in clearance, and you could probably cut your heat gun usage as well.
I used the heat gun on high, picked a warm day, and had the machine in the sun, heated it up for about 5-10 minutes above each wheel, and then used a 1"x8" board to start, then as I got more clearance, went with a 2"x4" eventually. You will have to repeat the process to get the desired clearance. Don't stop when you have just enough as the body will sag eventually, I'd say stop when you have about 2" clearance above the tires. The process will need to be repeated about once a year to maintain the clearance.
I think that your theory of using 20" tires is very valid, there's not much that the extra inch gains you in clearance, and you could probably cut your heat gun usage as well.
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