I've been playing around with various hot box designs for a few months & using a temperature probe I found that a light bulb design (5 lamps) without a fan gave too wide a variance of temperature within the box, 19-23F degrees variance in fact. Using a fan dropped this to 10-12F degress variance which for me was still inacceptable. In both cases, not surprisingly, the hottest areas were directly below the lamp.
Because of the high 'spot' heat I disgarded the lamp design & looked at a heater & fan set-up. A very good set-up would be a tubular heater with a seperate fan & a thermostat etc. My box has internal dims of 200x35x45cm (it takes two pairs of skis) which would require approx 300 watts of heat to maintain it at approx 70C/160F which can easily be obtained by installing a 4' 80wpf tubular heater. These are the types of heaters used in greenhouses etc so can easily be obtained from a local gardening store, although the quality isn't usually that great & the thermostats often won't measure at high enough temperatures. A better option would be a commerical quality tubular heater, fan & a thermostat from the likes of Watlow US which you should be albe to get for $100-$150 as the same solution from Watlow UK was about £80.
For the ultimate solution contact Mike at http://raceeffect.com
. Mike (who is Indy GS
on this forum) is now starting to offer for sale a scaled downed version of the heater/blower/control unit that he installs in his superb commercial hot boxes to give DIY box builders a commercial quality system. This is the solution I've gone for & the unit arrived just a few days ago. I haven't had a chance to install it yet but I've re-wired the control unit for UK 240V (it's either 110V or 240V depending on the internal wiring terminals selected) & fired it up on the bench & everything works superbly. Will post again with pics when it's installed & tested etc.