Well FlaBoy BH209 is basically non-hydgroscopic so the likeliness of it collecting moisture in your rifle is negligible. IMO removing any loose powder from a muzzy will create a mess no matter what kind you use. And especially an inline if you remove the breech plug and push it out though the back. My suggestion in getting it out the barrel is to shoot it off. Cleaning the breech threads would be a chore. Using Lane's tubes or similar is the best way to carry loose powder. You're also going to need a powder measure.
Loose powder is definitely the way to go. Pellets are convenient but no where near the versatility of loose. This is the measure I use: