For that trip, I recommend you do one of the following:
1. (Cheapest) - buy a decent, low-cost portable receiver which will receive SSB signals. The DEGEN brand models run less than $100 and have received very favorable reports. They're everywhere...check out eBay listings.
2. (Smartest?) - buy a used marine or ham transceiver for under $500, and install it so that you can receive well.
Notice that I did NOT include buying a good SSB receiver. That's because for the same money you can get a TRANSCEIVER which can later serve your transmitting needs as well as receiving. All modern transceivers have excellent receivers built-in. NO need for a separate SSB receiver, IMHO.
For a receiving antenna, you can just use a length of insulated wire, hoisted with a spare halyard.
Later, when you add an automatic tuner (about a $400-500 expenditure), you can set up for transmitting as well. For the 'alternate backstay antenna' just use a length of insulated 3/16" s/s lifeline about 40' long and put small loops in each end. Hoist one end with a spare halyard. Tie the lower end off to the pushpit on either side of the boat, using a couple feet of 3/8" or 1/2" poly line. Then, run a length of GTO-15 insulated wire from the lower end of the antenna belowdecks to the tuner antenna lug. Locate the tuner underdecks as close to the bottom of the antenna as you reasonably can.
By the way, RF grounds in IP's are pretty easy. The ones I've seen and done all have a s/s rub rail all around. All you need do is link them together electrically (usually there are 4-5 pieces overall), and use them for an RF ground or counterpoise. They work like gangbusters.
Just run a ground strap from the antenna tuner ground lug to the rub rail, using a bolt which passes thru the rail, thru the hull, and attaches to the groundstrap inside the hull. Then, run a ground strap from the antenna tuner's ground lug to the nearest bronze thru-hull which is not otherwise connected to the boat's bonding system.
Pretty easy installation. If you have time, and $$$ for the tuner before your trip, you could have an excellent SSB installation.
For WX, listen to USCG broadcasts several times a day on published 4, 6, 8, 12 mHz frequencies. These are also re-broadcast by WLO in New Orleans, and several ham nets (e.g., the WaterWay Net on 7268 LSB every morning at 0745EDT and the MM net on 14300 USB periodically during the day).