Now, if I may side-track your thread for just a second. Help me with your reasoning for insulating a keg for MLT vs. using a cooler. I ask because I'm starting to build my rig and I have two keggles and a cooler than I have been using for an MLT. It holds temps within 1-2° per hour with no input, and I cannot imagine why someone would want to use an insulated keggle and have to them heat the mash to maintain temps. Yet insulating a keg for use as an MLT is very popular. I must be missing something. Not trolling, just can't make the connection.
I use a keg MLT on a burner and since I'm yet to play around with step mashing, I can see your point. However, wrapping with 2 layers of reflectix holds the mash temp really well and I love being able to mash out without infusing.
If you know anyone that sews, you could get some Reflectix and wrap it in fabric with Velcro closures. That would be sweet for when you need it, and you could take it off when you fire up. The material could even be higher temperature proof.
I used a couple layers of the silver faced bubble wrap sealed with aluminum tape on my MLT. It was a bit stinkey the first time I fired it up, but now it works great! It is nice to be able to heat your mash water in the MLT before adding the grain at the start. It is really nice to start recircing with the pump and light the burner to mash out.
I use 3 layers of said silver bubble wrap insulation taped up with silver tape. I also found that putting a blanket on the lid helps. After 10 or so batches with it, the bubble wrap has shown some signs of melting/deforming, but it's held up pretty well. I covered up the skirt drain holes with silver tape as well because I found that fire/heat can shoot up through those holes and melt the bubble wrap. Of course, I have to be vigilant about not letting propane gas build up under the skirt with these holes closed up. No explosions so far!