Fuel Tank + AUX + Tool Storage?

[East_Bound]

What's up guys -

I realize how many aux/fuel tank threads there are on this site and am sure you guys are exhilarated for another one so here it goes...(Pics Below)

1971 Chevrolet C20 Custom Camper

So I understand the fuel filler on the cab is my main fuel tank and I understand my fuel filler on the bed is my auxiliary which holds one gallon? When I look under the truck on the driver side, I only see one big tank and not two separated. Is the auxiliary located inside the main fuel tank? How would I gain access to it if needed?

When I looked on my passenger side I thought I found another tank for fuel, but noticed on the outside there is a slot for a key, so I would assume that is the tool storage that is noted on the inside of my glove box?

And while I'm at it...My AUX Filler cap fits perfectly while my main fuel tank cap only locks on one of the tabs so I get to look really classy around town by locking it down with duct tape. Is this a cheap universal cap someone bought over time?

I found a cap online. Is this the right one?

http://www.partsgeek.com/catalog/197..._tank_cap.html

I noticed the top two caps up top look and sound identical..What is the difference? Thanks in advance!