Just finished this job. I used the 1.5" diameter sleeve from Spruce.(pricey) I slit it along the length, turned it 90 degrees and wrapped it around the cube. Secured it with a metal firesleeve clamp around the middle and tywraps at each end. I also used a short piece of small diameter sleeve at each end to cover the flare fittings. You will need to make a cut in each corner to allow the tywraps to pull the ends in snug.
I used the high temp permatex to seal the seams. This also firms it all nicely, and holds in any baggy bits.
I was surprised how well it worked out, I was anticipating a bit of a struggle!
Mind you, I haven't flown yet.