Hi Jim,
 
First of all, don't put your shells in the sun, even for only a week.
Secondly, you really do want to get all of the animal out that you can.  As the
animal decomposes, the acids that build up can damage the shell.  This has been
discussed in the past, so there should be some really good suggestions in the
conch-L archives about how to clean and protect your shells.
 
The URL for the archives page is:
 
http://museum.nhm.uga.edu/CONCH-L/CONCH-Larchive.html
 
Unfortunately, they aren't searchable by subject for the entire history of the
list, so it might take some time to find specific articles.  Does anybody know
for which dates he should look?
 
Travis