I just measured the internal volume of the boat below the bunk boards. This does not include the area in the stern or the two forward most compartments, only the area in the cabin. I used V=.5bxhxl and came up with b and h by measuring the mid point values for each space. Excluding the foot well, it turns out to be 346 liters per hull. This equates to 16 medium size dry bags or 5 large (read expedition) back packs per hull or a total of 10 back packs or 32 dry bags. This is a lot of stuff. Between the two hulls, if all this was water it would max out the amount of weight Wharram suggests you can load in a Tiki 26. If you use a factor of .4 (taken from volume of the big backpack and the suggested carrying load weight) then this below bunk area is where you would store 40% of what you bring on a trip. But this should be modified as presumably you won't have a tent and light things like clothes, sleeping bag and pad would go above the bunk boards so perhaps the area below the boards will carry more like 60% of your stuff by weight. All these issues are important when it comes to thinking about the intended expedition.....