If it truly is 18.5", a 30 gallon drum should fit right in for a slightly taller 18.5" WSM. Maybe 3 cooking grates!
Would have to sturdy up the legs for that though.
Modded Brinkmann Gourmet. Basic UDS. Rescued 22.5" OTS. SJS Mini-WSM. Stubbs. B&B Oak Lump.
Cannondale 2009 F8 (for burning off all the great BBQ)