I use some nice thick custom board with a recessed square section for the fresnells to fit into, and then screw into the recess area, dont need glass stays pretty flat, using glass reduces light output so you wanna stay clear of that if possible.
ill post some pics to show what i mean in a minute
frame - the recessed edge seems to be enough to keep it straight, and the screws hold it there... although u wanna make sure you have your box cooled efficently (im using 1x120mm) so that the fresnells do not bow because of heat.
I built a 3 sided U Channel out of 1/2" MDF that was big enough to hold my LCD/Rear Fresnel/IR Mirror/UV Protection all in one unit.... then I made spacers from wood to fit between each element to make it snug... I found this to be an easier way to ensure that every element was perfectly aligned a parallel than making individual frames for each element. Currently I have the front fresnel on its own frame so I can do Keystone correction, but this may go away in the future, and Ill just build one big "Imaging Unit" containing everything.
i think they mean, U channel for the air to travel through you know, lilke in the lumen lab plans, air is drawn from top down to bottem, goes under LCD, and back up past the lcd and out past the top of the 2nd fresnell, cooling all three items in 2 passes.
im simply assuming here tho, thehehee more of a "V" channel.
This is how mine works as well, keeps everything stone cold, have the rear fan sucking, and i find it only needs a single 120mm fan.. and everything stays nice and cool.
air is drawn out of the box by the fan at the rear, goes through the LCD/frensel configeration, and enters the box where that black square is between the top fresnel and the triplet, air goes from front to back, through the channel between the fresnel and LCD, cooling everything similtaniously and effeciently.