Cory - notchin' isn't too difficult - the issues are addressing the stresses in that area (and accounting for trailering if you're going to) in the reduced corss secion of the frame -- that's why most places will use 1/4" materials...
The newer high-strength fromaes don't take too well to welding (localized heats) so they'll need bolt-on notches with pretty tight tollerances -- I've had great success working with bolt-in notches that sandwich the existing frame for thhe new stuff...
If you're working in the old world - building/welding one on the frame is doable - and pretty giggered easy - again, you address the strength issues of reducing the web-area of the existing frame and only put in the clearance that you need (where you need it) . (see
photos.yahoo.com/lo_burb for a welded insitu notch on a burban)
really the costs associated with a pre-fabricated notch are not too bad and the pre-fab will take much of the stress calculations and placement issues into consideration. the notching is something you really won't wanna mess-up and you'll need to know where everything will be ending-up before you start...
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