Currently I have 6 250's in the shop that I instruct in. I have found that using a piece of angle iron to help fit the 2 can together is beneficial. Pre cleaning the cans with a stainless or brass wire brush is a must. My students practice with 1/16" 2%thoriated and we use 4043 .030 spool gun wire. After the 2 cans are tacked, the arc must be concentrated in the center of the tack to begin the welds. I have found if the cans are not cleaned properly by remiving the clear coat the arc will take the least path of resistance and melt a hole in one of the cans. A steady hand is a must, and the rate at which the filler metal is added is essential.

Hopefuly this helps,