is there a way to permanently put my Bluegreen points into RCI in a way that I can build up a balance to save for a specific stay?
As others have said there is no permanent way to have your points put into RCI. And if there was, there would be no way for you to go to any BG resort without paying the high RCI fee.
But I understand there is a workaround that might help you achieve your goals when you want to trade with RCI and do not have enough BG points. The workaround is to make an RCI reservation using X BG points and then after a day or so, cancel the RCI reservation. Your BG points stay with RCI, they do not go back to your BG account (which makes sense since the BG week given to RCI might already have been reserved by someone else). Then when you get your next batch of points, make another reservation using Y BG points and then cancel. Then you hopefully have enough BG points (X + Y) deposited with RCI to get the higher point reservation you want. I have never done this and there might be a "gotcha" in there that I don't know about, so be sure that you hear from someone who has actually done this before you try it.
Another method is not a workaround. When your points are added to your account then pay the next year's fees and borrow those points. Now you have two years of points in your account and you can then get the higher point value RCI stay that you want. Of course, in one year you have to pay fees twice, but then it is once a year after that if you keep borrowing.
The third method has already been mentioned many times. Buy resale points. You can get them for pennies on the dollar (if that much). And since you have Trust Fund E, Sales Type A, you can buy any Trust Fund E points. They don't have to be Sales Type A. BG will convert other Sales Types in Trust Fund E into Sales Type A. But do not buy in other Trust Funds because those will NOT be converted. (One proviso, you might find a resort,unit,week you really want to use using the 13 month rule. Then paying a higher MF for that week might be worth it to you.)
Charles