Mine have never cracked in over 5 years of using meth on DSM's and the Evo, but I always use vented caps. Pressure is going to build in there and the caps are weaker than the tanks (thank goodness or else the tank might split). Here is a new product to check out, the strainer -
http://fluids.flambeau.com/component....html#strainer not sure how you fill up but this is chemical resistant. I love mine. I use a battery operated pump to pull from a 5 gallon jug to my container. The caps are here -
http://fluids.flambeau.com/caps/caps_2none4th_inch.html Get a vented, you won't smell it in the car, and it won't crack (at least mine hasn't in over 2 years of using the same cap on a couple different containers)