OK, I did some more homework. I got Harold Barre's book "Managing 12 Volts" from the library. I also checked Interstate's web site http:/www.ibsa.com/www_2001/content/products/date_codes.asp)
to learn that the battery was made 5/1995. So I guess it lasted a long time. This site has a decent explanation of the battery date codes.

I borrowed the Fluke DMM from work (which measures millivolts).

According to Barre:

OPEN CIRCUIT VOLTAGE STATE OF CHARGE
12.6 or greater 100%
12.6 - 12.6 75 - 100%
12.2 - 12.4 50 - 75%
12.0 - 12.2 25 - 50%
11.7 - 12.0 0 - 25%
11.7 or less dead

The old battery had about 12.0 volts on it, and it dipped significantly with light loads.

Although I would like to have put in 2 6V golf cart batteries as Barre recommends, I decided I didn't have time to get into that project before our week in the 1000 Islands next Saturday. There's not room, and I would probably have to mount them on the tongue.

I picked up a group 27 deep cycle marine battery at Sams Club (Stowaway 27DC-5) for $46.99 with exchange. It's only 95 AH. I was worried that it might not fit, but it fits nicely. Then I realized I could have brought the battery tray with me to check :-(

While I had the DMM, I measured the current draw for several items in the trailer:

roof fan 2A
ceiling light (1) 1.3A
flourescent bathroom light 2A
bath/fridge fan 0.75A each
refrigerator 8.5A
Thetford toilet 4A
water pump 4A (not measured, but from the label)

I didn't have time to try measure the heater fan.

The numbers above will be useful for the "Determine Your Electrical Requirements" section in Barre's book. I will attach my Excel spreadsheet once I figure out how to do so.

The new battery had a solid 12.6V as installed. I needed to add a little water and am now topping off the charge (13.76V last time I checked). No more bubbling.

Last comment- check those date codes when shopping for a battery. Of the batch at Sams, I picked the one built JUL 01. There were some as old as MAR 01. In Wal-Mart, there was one 3-00. A year and a half on the shelf!

UPDATE 8-20-2001

Good news & bad news.

The good news is that we went 7 nights on the new battery after driving 3.5 hours with the fridge on +12V.  We were conservative- 1 or 2 lights on maximum, and only when we were inside.

The bad news is that on the drive home with the fridge on +12V, the battery went so dead that the fan quit running and the test panel wouldn't work.  The battery recovered after a few hours, but I expected the Safari to be charging the battery on the way home.

Need to check some voltages with the Safari hooked up.

The battery recharged OK on 115 VAC.