you cut the tubes so the fit up is very good down to 1/8 then some sealer to seal them if you glass them or tack weld them every time the 1/4 flexs it will pull a dent or line .as for fitting the tubs i done some. it is one of them deals on how i could tell you how i do them by taking to you .but my typing skills are not that good or spelling so for me putting in the tubs would be e z er for me