After trying a resistor heated hot-end, I got a little concerned with the tight fit in the standard mendel X axis carriage. I tried Bubak's OpenX Carriage (http://www.thingiverse.com/thing:6278) and I really like having an open center.
In my config, I've got the dump zone on the far left and the OpenX won't let my extruder reach it. I started playing with this idea for a very lightweight carriage that would only have what I needed. Since I use mechanical endstops, it has no holes for mounting flags and is optimized for a horizontally mounted Wade's extruder.
This design is narrow, light, and uses only 8 bearings. (It might be possible to fully constrain it with just 6 bearings by eliminating one on the bottom of each rail.)
Since this is just an experiment, I'm marking it as a work-in-progress and I welcome comments.
So far, I've only printed a couple small parts with it but it seems very light and tight.
carriage3.stl is a revised version to deal with a couple problems:
The belt is uncomfortably close to the screw heads on the unclamped rail. In my setup, it barely touches, but any rubbing is probably too much. This version recesses 4mm nuts in the carriage and expects a 4mm bolt instead of socket head cap screw. The direction of the bolts is reversed.
The posts for mounting the extruder have been widened and are a little taller to give some additional clearance for the big Wade's gear.
I added a gusseted side on each end to stiffen the carriage.
I'm still planning to redesign the clamping rail to add a tensioning screw for the belt.