I guess my first question is where does the extreme concern for a rusting bore come from? Are you finding signs of rust after they've been cleaned and sat for a while?
I can't speak from any kind of experience on the inline, especially if you're using BH209, as I don't own one and they just simply don't interest me. There are tons of folks here that do use them and I expect they'll chime in. I believe it is best to use an actual solvent like Hoppes with BH209 like you would on a modern CF rifle.
I do shoot a fair amount of real BP in my TC Renegade though. I've caught it starting to show rust only one single time...well, besides flash rust if I clean with warm or hot water I should say. After shooting I remove the barrel, remove the nipple and then stick the nipple end of the barrel into a small bucket of room temp water with a couple drops of dish soap. I really feel that water is the absolute best for cleaning BP fouling. It is abundant and cheap too. Doesn't hurt a thing as long as you make darn sure you get the bore very dry after using it. (Note: If you are a married fella, you may have heard about doing this in the bathtub. DO NOT do it in the bathtub!...especially if you're planning some romantic gestures later in the evening. Just getcha a bucket). If you don't have an easily removable hooked breach, then one of those kits with a tube that threads into the nipple hole will get it done. I wet a cleaning patch and then run it up and down the bore multiple times with the ram rod and a jag holding the patch. It will syphon the water up higher and higher into the bore each pass until it is pouring out the muzzle end each pass. Then I swap out the water for just plain clean room temp water and do it again to rinse out any BP residue and the soap. (Note: if I use hot or even warm water I see flash rust every single time on the first drying patch I run. Room temp or cold and it isn't there, but hot is really useful if using a chap stick style patch lube such as bore butter). After the barrel has been rinsed I tip it up so excess water will run out of it. I dry the outside of the barrel and use canned air to blow moisture out from around the tenons and sights. Then I run dry patches down the bore until they are coming out dry. (IF I'm seeing color on the drying patches I will wet patch - dry patch until that quits happening, I use Hoppes BP solvent & Patch lube on the wet patches.) Pour some denatured alcohol through the nipple hole and let it run out the barrel. Then another dry patch. Then I run a patch to the bottom of the bore and leave it there and blast some air through the nipple hole and flame channel. Remove that patch, blast some more air, and run a couple more dry patches for good measure, you absolutely want it dry. Now it is ready for rust preventative.
I started out just coating it with bore butter. Never found rust. (I truly believe the folks that have found rust after using bore butter simply didn't get the bore clear dry before applying it...or they think they saw rust when in actuality it was the dried out bore butter. It turns very brown after it has sat for quite a while. Any animal fat should work too, as long as it blocks oxygen from getting to the walls of the bore)Then I read about using oil and just swabbing it back out before shooting by running a patch of 91% or better alcohol, so I started storing it with a coating of Hoppes gun oil. (Stored it barrel down always so none would get into the flame channel). Never found rust. Then I read that gun oil isn't a great rust preventative and is mainly just for lubing, so I switched to Ballistol. Successful the first few times...but then I did find rust! It had sat for about 4 months since I'd last shot. Very mild thankfully, but it was there. So then I switched to Barricade. I've never read a bad word about the stuff, and I like that it dries into a film. This means I don't have to swab it out before shooting, I can actually leave it protecting the bore and load up for hunting and know there is still rust prevention in the barrel. Never found rust with it to this day.
From all the rust preventative switching above you could probably surmise that I was a might worried about rust too at the beginning.
I don't worry much about it anymore, I've only ever found rust the one time, but that don't mean I just ignore the possibility. After cleaning and applying Barricade, I do go back a week later and run a patch to make sure everything is good. After that I will check once a month until I shoot again.
Just running a clean, tight fitting dry patch down the bore on occasion will tell you all you need to know.
Now, go make some smoke. It is just sacrilege to not enjoy shooting your muzzleloaders whenever you fancy to do so.
