Everyone says you need to keep your epoxy warm to make it easy to work with and prevent it from absorbing water.  Given that my workshop is in the basement, and dampness would always be present, I decided I really needed to build one.  Starting with a piece of leftover 3/4" treated plywood, I added some pieces of ripped-up 2x6 to leave spaces on the inside so I could insulate the inner surfaces.  I mounted some leftover wire shelving, two old light fixtures and a fan I found at Menard's for $3.   The only thing I had to buy was the thermostat, $13, and of course the pump, which bolts to the bottom with some wing nuts so I can take it out if I want.

As you can see, it's sort of big.  However, I have just about all my supplies in there so everything is warm, dry, clean and ready for the next layup.  The milk jugs have micro and flox in them, again, inside the box to stay warm, dry and clean.

Here's a picture with the lights on.  Some builders I have visited have stated that with MGS epoxy the hot box is completely unnecessary, and I have turned the temperature down significantly (I now keep it at about 75° F) and have noticed no difference in wet-out, curing etc.  I could probably do without it altogether, but as stated above, it keeps other things like my flox and micro warm (not hot) clean and dry.

You can't see the setting of this thermostat, but, it's set to 70 degrees.  For whatever reason, either because of the fan or because the thermostat "bought the farm" it stopped working properly.  I have had it set at 70 for about a year and a half, and, always wondered why it seemed so warm in the hot box.  It was too warm - see the next picture below.

When a new, cordless, L.L. Bean inside/outside thermometer arrived as a Christmas gift for my wife, I inherited the old thermometer.  With a large LCD display and a 36" remote temperature sensor, I knew it would work great for my hotbox.  It became absolutely clear that the thermostat wasn't working properly, even if this thermometer is off a couple of degrees, it's a bit warmer than the setting I had on the thermostat.

I have since taken out the fan, disabled the thermostat and went down to one bulb.  After several experiments with different numbers of bulbs and different wattages, one 100 watt bulb seems to hold the temperature where I want it.  It stays at over 100 degrees, but, if I went much lower than that in wattage it takes the box too long to heat back up after you open and close the doors a couple of times.  I am very happy with the simplicity of this new setup, like having the thermometer on the outside so I can monitor the box without opening it, and, my light bulbs last a lot longer because they don't go on and off every 15 to 20 minutes!  It seems to keep the crystals in the hardener side of the pump down better than the other way as well.  Makes sense to me - not so much air blowing around and not as much temperature cycling.  I even added some additional weather stripping around the doors. 

Eventually (after about a year) I started having troubles with the paint can I put on the hardener side.  I had a valve, on the top, that was too stiff and I was concerned about the hardener eating away the inside of the can or the coating that those kinds of can usually have.

Here's the inside of the lid.  You can see that the hardener was starting to do some funky things.  I wasn't having any epoxy trouble, since I check my layups regularly, but now that I see this lid I'm glad I changed out this container.

I bought a Rubbermaid container and drilled a hole in the right place in the bottom to mount it.  Nothing too critical or specific here, but, I found one with a flatter bottom, square so it fit on top of the pump nicely and not too tall as to force me to move shelves in my hot box.  Further, I got one with a simple snap open top.  That way, I can pop it open when pumping, but, snap it shut again when the pump sits for a while to keep more air out of the hardener side.  I do like the larger size, also.  I can put two whole cans of  hardener in at a time (one fast, one slow) without having to measure amounts.  Sure, I could use a little more or less than 1:1 with fast and slow but I have no reason to.

To fill either side, I just move the stuff off of the shelf above the pump.  Swing the shelving material up (it's only fastened in the back) and fill away.

I have since added a piece of vinyl siding material as a shade between the light and the hardener container.  Some builders have said that continuous exposure to light can be bad for the hardener.  This way, it gets reflected/indirect light but not direct light.