Under the stairs...

Hey, what's up everyone? I'm new to the boards here and I'm looking for a little help with some bass traps. I've been through a lot of information here and many other sites and I've found a lot of helpful stuff but, I'm looking for some expert advice on a few specific things. I've got a small space that I am using for my home studio and I'm having all sorts of problems with the low end, standing waves, etc... Budget isn't an issue at the moment and apparently there is a supplier in my area for insulation materials, Paragon Pacific in Portland, OR. I'm also capable of building everything myself. Here is a drawing of my room with dimensions. My desk faces the north wall, which is up in this pic. Behind where I sit is the stairs to and from the basement. the underside is just an open cavity. I need bass traps back there and I'm trying to figure out the best way to go about it. It's used for storage right now and one of the issues is, it needs to remain a storage area. There is only one corner that I could straddle and I don't think that will solve the entire problem anyway. So my idea is to turn the entire cavity under the stairs into one big bass trap with storage inside... The first part... Forgive me for I do not know what this kind of trap is called. But basically, there would be three boxes with hanging slats covered with insulation inside. One of the things I need help with is what actually goes inside the box. I have seen pics of a few of these and it looks like they get lined with mineral wool (or something similar) and the slats get covered with some sort of fluffy insulation. Also, should the hanging slats be different sizes? Can someone please help me get started in the right direction? Second... I would like to close off the space so that the storage area is hidden. So I would cover the entire opening with panels. Two of them would be on hinges to make doors to the storage area. The question is... they will be about 2.5' away from the wall behind them, will they do their job in that location? What type of materials should be used, thickness of insulation, etc..? The third part of the question... Assuming the first two things will work, durability becomes the next issue. There is a sliding door to the outside right next to all this and it is a high traffic area. I need to make sure nobody can fall through these things. Should I cover everything with wood slats or pegboard or something? Aesthetics is important and I like the look of staggered wood slats but would something like this hinder the performance of the bass traps? I guess that's all I've got for now and I hope it all makes sense. Any help I can get with this is very much appreciated so thanks in advance. Mike