Don, just had a BIG discussion with one of the other DM's at the shop about this. You know I have a probe, so does he. I just finished my heliotrox cert and will probably do the majority of my diving in doubles from now on. I do however have a DSS doubles set up for that. I also have a DSS single rig as well. I have not dove al80's as all my tanks are steel. A set of 72's, 85's, and 95's as well as my singles. Two more 72's and two hp80's. Having said all this, I would strongly recommend you NOT put doubles on the probe. While the 80's buoyancy characterisitcs are different that is still alot of mass to put on there. I have not seen the adapter as yet but for 119 bucks you could add 200 to that and get a used BPW in very good shape. Now to the reasons why I don't recommend the probe for this and especially for travel. One is the depth compensating cummerbund- while it's nice and does work with singles it can also allow the mass of doubles to move more than they should. Not good. It also inflates on the sides and with double tanks this could have the tendency to tip you backwards farther than you would like on the surface. If for some reason one of the shoulder straps would loosen it could become very unstable. THis bc was never designed for doubles. the adapter is an attempt to let people do something they may wish to try but not a good idea IMO. I rarely dive mine anymore. And since I'm doing the NAUI DM crossover I don't really need to except in the pool with students. ANd after the first session my NAUI instructor allows me to use my BPW. and doubles if I choose.
As for travel and doubling 80's unless you are taking your own with you very few places rent doubles that I'm aware of for recreational diving. If you do get 80's they would most likely have to be set up as independents and would significantly and to your gas management task loading. Not a big deal if you have the training and experience with them but still more involved than diving dbls with a manifold and isolator.
You also need to get your regs for this and correctly configure them. DIN or yoke? most people diving dbls use DIN. Most rental ops are yoke. Adapters are available and work. But for me I have a seperate set up for single yoke tanks that consists of a DX4 w/ an alpha 7 and swivel octo or my blizzard with standard octo.
Inverting the tanks can make it easier to reach the valves but is generally not done because of the risk of damage to them when getting in and out of gear. They use manifold guards in the UK regularly for wreck diving and some cavers use them but they are designed to protect against little bumps in overhead environments. Not to support the weight of the tanks. They are also usually clamped on. Ops might not let you bolt things to their tanks.
I'm also curious as to what ops would let you do profiles long enough to require doubles. Most limit you to an hour or less and unless you are going to depths in excess of recreational limits an al 80 should be fine. On Monday I'm doing lake Erie. This is a tech trip. We are doing a wreck in 165 ft although I'm not planning on going deeper than 155. Not interested in looking at bottom mud anyway. Dbl 85's pumped to 3000 psi with 21/25 trimix. Bottom time of 18 minutes in 40 degree water. Deco is going to be around 38 minutes according to v-planner total gas usage will be around 115 cu ft. I'll be carrying close to 210. This is however a planned technical dive with deco. Unless you plan on running similar profiles you don't really need to double up on tanks. I ran a simulated dive to 130 ft for 10 minutes on 25% nitrox and only use 39 cu ft of gas. If you are doing reefs and staying shallower than 60 ft or so most ops won't let you stay down long enough anyway. In the keys for example it's one hour and back on. On a 40 ft reef I'm coming back with 1500-1800 psi after 59 minutes from a 3000 fill on an al80. There's the other side. WHo is going to dive with you and will they be diving doubles? If you take a tech op out chances are they won't let you do doubles in a rig like that anyway without some type of tech cert.
Bottom line- Doubles are great! I love diving them now. Did a 40 minute dive in a lake last monday with my 72's in a 5 mil. 49 minute dive started with 2500 psi. I still have 2000 in em. But I'm doing this in a rig designed for them. If you want to do doubles go for it. But get a BC that is designed for that. ANd take an intro to tech course that will help you with starting out. I promise it will be well worth it. Warning though- once you start down this path you may not be able to turn back. Your probe may become an expensive dust collector like mine. You'll start buying more tanks, a dry suit, can light, argon bottle system, an on and on. Expensive yes- but one hell of a ride!
