Here are a couple of functional mods (actually add-ons) I did to my offset...
Added a drip lip between the channel and firebox (channel pic and firebox pic above). Instead of having to weld it in there, it is a fitted double angle (hangs off the edge of the channel with a piece going up that acts as the lip/dam). It is also removeable for cleaning this way.
Added an expanded metal charcoal grate on top of the log grate. The grate is fine with just splits, but if I put down a charcoal bed the charcoal falls through too quickly.
My MacGyver solution for using my warmer box as a vertical charcoal smoker. Drip pan in the bottom of the channel to act as an ash tray. Expanded metal ring for a riser. Expanded metal grate and another ring to hold the charcoal. The ring on the bottom is a bit taller, so one or the other is used depending on how much charcoal is needed. The grate is the one from on top of the log grate, and the drip pan is from the main chamber. Making it modular (AKA MacGyver style) actually works better for multifunctioning the equipment (can also use the rings in my charcoal box for smaller loads).