First off, the bearing surface of the barrel extension flanged lip to the upper barrel socket face, with the barrel nut holding it in place at 35FTlbs, but not to exceed 80ftlbs to get the spine void to index with the upper tube channel is more than enough for any SBR rig.
On longer barrels like say a 20" or longer such as a 26" long bow in 308, here the loctite between the barrel extenson sides to barrel socket to fill the void will help to minimize the differances in barrel harmonics instead (using more of the upper barrel socket as reinforcement.
So back to locktite, and since you are trying to fill the entire void area of the barrel socket side walls to side walls of barrel extension surface to face of receiver extension on the lug side, barrel socket and it lip are left dry (cleaned with acetone), only the outer lip flange and front of the barrel receiver is moly greased to get the correct torque, and barrel nut is installed with receiver lugs correctly indexed.
Now muzzle down after barrel is installed, here is where the wicking loctite comes into play, to fill the void completely between the two (air will bubble up and out) and allowed to set up, verse going in wet on the two surface with loctite, installing the barrel in the upper level, and ending up with air voids in the loctite between the two isntead.
As for barrel nut to upper, and even tube to barrel nut on DCM float system, the upper receiver and barrel nut threads need to be mated to each other with moly to start with (barrel nut to receiver), then moly removed, and you can go with a loctite to Glue the three together in the end. Again, on a DCM float tube, you have the barrel nut that is tighted to the upper receiver barrel socket, then tube section that is tighten to it, since the outward appearance of the rig has to look like a service rifle in the end. Also, with the amount of torque you will on the front end via sling, so it will end up with the float tube thread twisting over the season.
Bluntly, if you wanted to loctite your rig now (for grins, since it not going to make a difference on your SBR barrel if the barrel nut is correctly tighten to begin with), could just use brake cleaner to hose out the void area now between the two, and them using wicking loctite to fill the void with the muzzle straight down.
Just keep in mind that you will be filling the receiver socket channel for the barrel extension pin with loctite, and going to take a lot of heat to break the locktite down, including around the receiver pin to receiver socket pin channel, before you will be able to pull the barrel.