This is really more of a network engineering issue, I don't really see how Perl enters into the security much at all. Lots of good suggestions in previous posts, here's my distillation of the ones I like and my own spin:

1. SSL encryption (or better) is absolutely required. Whether you do WEP on top of that or not is up to you.

2. Since the wireless protocols are sniffable, you should assume that your wireless network is 'outside' just like the internet is 'outside'. A firewall is a good start, a firewall with a DMZ for the web/db servers is even better. If you tell the firewall to simply drop and ignore any traffic that isn't a VPN, most attacks will be ignored.

3. I really like using keypairs instead of passwords for something like this. For the truly paranoid, insist on montly maintenance on every laptop, where you watch it do a full disk scan for viruses, malware, unauthorized software, etc., and also REPLACE the private key. For maximum paranoia, restore a disk image each month and then replace the key. (Probably takes about as long as the virus scan.)

4. Don't forget to put at least a software firewall on the laptops, again configured to ignore anything incoming that isn't part of expected VPN traffic.

5. If do the firewall and secure VPN things on both ends of the connection, the client and server neither know nor care that they happen to be sending bits over the air instead of copper. Keeping the OSI layers separate helps keep down suprises.

Good Luck!
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Spring: Forces, Coiled Again!