Mark, my xg 110lc is the exact same as your 135.
The xg's main heat removing fans are located at the rear on both sides, so here's the best way to do it.
1) Mount your projector were you want it on the ceiling.
2) Go to your home do-it -yourself warehouse and get a 6" long piece of 4" duct and a 4" tee.
3) stick the 4" up against the ceiling, centered at the rear of the projector, make sure the closest part of the duct is 3" behind the projector (your 5 BNC connectors have to have room) draw a circle, and cut it out.
4) ductape the 4" tee to the piece of duct, and stick the duct up into the attic...I screwed a piece of 2X4 up there right next to the duct, then screwed an "L" bracket into the 2X4 and ductaped the duct to the "L" bracket...that'll hold it in place at the projector end...make sure the tee is positioned so when the evac system is running, it's pulling the air from the sides of the pj...in other words the tee's openings are to the sides. Chaulk around the duct.
I used a couple elbows and 4" flex duct to run over to my air conditioner return box, cut a 4" hole in it and ran the duct into a 70 CFM bathroom fan that I set in the bottom of the return.
By putting the Tee at the rear your working with the projectors cooling system. It'll push hot air out all those vents along the sides at the rear. The Hushbox evac system will pick it up as it exits the projector.
You can also make the pj's cooling system more effective by removing the plastic side panels and ductaping all the openings in the sides of the metal chassis. seal around those fans too.
The only place I left an opening was on the left side (looking at front) there's a set of high voltage coils...I left the front half inch of that large opening...the rest of that opening (and the one on the other side) I plexiglassed. That opening will allow air to be pulled over those coils, MORE efficiently that if the whole thing is open...if the whole things open the fans pull from the closest point, very little air actually flows over the coils, but close off most of the opening and now it has to pull air from in front of the coils, so it flows over them.
The XG's cooling system is very inefficient as it is...it almost seems like an after thought.
With all the ductape mods, and in it's hushbox my pj runs 9 degrees cooler than when it was unmod'ed.
You can buy a $10 digital thermometer in the hardware dept at Wal-Mart. It has a tiny remote sensor, if you mount that on top of the XG's swing down panel (that puts it inside the tube cavity) it's got a 10 foot wire, so you can mount the readout on the outside of your hushbox. This will give you some base readings to work from...it's also a good idea to have those readings once the hushbox is in place.