Sean and Kelly,
I'd thought I'd combine my response to both of you.  The box is made by 
Rubbermaid.  The only numbers/letters on the box were as follows:  215A 
was on the bottom of the main box and 215B was on the inside of the lid.  
I hope this is the serial number you were looking for Kelly.
Here are the specs for the box:
The interior volume is 29" long X 14.5" wide X 12.5" deep = 5256.25 cubic 
inches = 3.04 cubic feet.
Sean, while I wouldn't call it waterproof, I think water resistant would 
be a fair assessment.  The only holes are up underneath the handle (small 
ones, maybe for air pressure to escape or a little bit of ventilation).  
The lid seals around the edge with a "tongue and groove" type system.  
The lower "tongue" sticks up 5/8" and fits in the "groove" on the lid.  I 
have driven through moderate rainstorms with no water breach.
It has 2 big clasps attached with metal pins and the hinges are 6" wide 
with metal pins.
Color:  light blue.
There is a hasp for a lock.
If I were to put the box up on the roof, shove it all the way back and 
into a corner, there is this much space left:
Between the front of the box and the front of the luggage rack well there 
is 6".  Between the side of the box and the side of the well there is 
18".  Quite a bit of space.  I can fit the box, one of the squat 5gl. gas 
cans, my 18 X 21' tarp rolled-up and my 6'X6' piece of Astroturf (front 
patio!) rolled-up.  I criss-cross bungie cords over the whole thing.  
Very solid, no movement at all.
I usually only keep my pots and pans and canned goods in the box, so I 
don't mind it sitting in the sun and frying.  Not too valuable in case of 
theft :(
One important note:  when loaded the box is heavy.  This makes it hard to 
put up there and esp. hard to take down.  One solution is to face it 
backwards and access it from the poptop.  Obviously it has to be popped 
to do this, also, it can still be a little awkward to reach out for heavy 
items, but it can be done.
Usually, if I have the room, I just put the box inside.  It makes a great 
footrest for rear passengers.  Outside it works great as a table or 
chair.  If you happen to run into a bunch of people, and you just happen 
to have a bunch of beer, it can double as an ice chest.  Not that this 
would ever happen ;)
Personally, I get tired of shuffling through my little cupboards amongst 
the food to find my pots and pans.  I put all my kitchen stuff in the box 
and use the cupboards for food.  
At least around here, these boxes are fairly common.  I have seen them in 
many sizes, some look like they would completely fill the rack.
The $10. I paid was a sale price.  Probably they go for $15. to 20. normally.
Hope it helps!  I had to dig it out anyways for my upcoming trip (only 3 
days, but who's counting :)
Charles
'83.5 Westy
'69 280 SE (back from the grave)