Hi Mrbadexample, love the name by the way.
I have constructed these barrel bogs in the past, and my avice would be as follows.
Aim for a substrate depth of 12" minimum if possible. 16" or deeper works well.
Drill a hole in the bottom of the barrel for drainage (stops the wood rotting from constant moisture retention so it lasts a LOT longer) .
Line the barrel with pool liner or similar cut to shape, this also stops the barrel from premature rotting.
Cut a couple of slits in the liner about 4"down from the to prevent innundation, you needn't do this if you can regulate the water level some other way.
Place an upturned bucket with holes in it in the bottom, or large plastic plant pot, to act as aresevoir for the water, and save on the substrate mix volume as it can get expensive.
Cut a piece of inch and a quater drain pipe to the same depth as the barrel and put it up one side. This acts as a visual aid to the water level and can be used to syphon out excess water in winter or whenever if needed. and can be used to water the barrel if you dont want to top water the plants.
Place barrel in its final display position, full sun if possible, place on brick if preferred to stop the bottom rotting from being in contact with soil or grass.
Mix your substrate, say 50/50 mix perlite and peat or 50/25/25 peat, perlite and sharp sand (horticultural grade) and fill your barrel.
Gently water with rain or RO water and mix to moisten the substrate (just moist not wet).
Tamp down gently and refill as necessary.
Get a selection of temperate pings, and sundews, some VFTs binata, capensis (they are hardy in my midlands bogs) and loads of my favourrites, sarracenia.
lay them out on top of the barrel to get a pleasing arrangement then plant them.
Put on some sphagnum moss as a top dress if desired.
Water with rain, distilled or RO water, to about 4" below the soil level.
Sit back, take photos, pat yourself on the back for a job well done and get ready to be rewarded with a beautiful display.
Once you've done one you will want to do more! its a bit like embracing the dark side
Hope that helps