You want my opinion?..... OK here goes.
A rollcage is a safety item, not a cosmetic or false-confidence item.
I never understand the comment that "I don't plan on rolling hard enough to need DOM" or such nonsense. None of us can predict the extent or severity of a rollover or crash in advance.... Nor can we negotiate for a smaller disaster because we "only built the cage with HREW". DOM is a stronger material and gives you a higher margin of safety when the unexpected happens. If you ever got seriously hurt (or hurt one of your passengers) I doubt it would be much comfort to know that you saved a few hundred bucks on tubing....personally, I'd want to know that I gave myself the best possible chance to escape without injury.
There are two objectives that I hear you talking about with this cage.... Protecting the soft, squishy occupants and stiffening the chassis. IMHO, protecting the occupants is the easier one.
Stiffening the chassis in a meaningful way will require you to build tie-ins to the frame in the engine compartment, not just underneath the cab. To improve torsional strength, you need long triangles from high spots on the cage down to the framerails...and you're going to need to "short-circuit" the flexible body mounts as well. You can't add stiffness to the frame if you've got a bunch of rubber or poly in the middle of your structure.
Look at how race car rollcages are built, especially the engine cradles and the way they tie in the upper rollcage to the frame near the rear axle. My guess is that your shop will want to do something similar if you insist on more stiffness. Maybe bring them a few photocopied images of your Blazer and ask them to draw where the tubes will go.... It's important to understand a bit more about where they plan to put tubes or you might be disappointed on the day you pick it back up (and give them a big check). It's possible that you are going to lose a lot of utility and seating area in the rear once they start dropping tubes in the places where they work best.
Keep in mind that having a safe, strong cage is street-driven vehicle can be a real hassle to live with. Climbing over cage bars, hitting your knees on them and the way they block access to things (like window cranks and glovebox doors) can really spoil your enjoyment of the truck.
At best, the cage will be a compromise between utility and function... If you go back and read my thread in the time period when I was building my cage I think you will see that I struggled with these tradeoffs quite a bit. You need to decide for yourself how radical you want the cage to get, and how much inconvenience you are willing to tolerate as a result.
-G
I'll give the guy a call today and get an idea what to 6 point DOM cage with sliders and engine bars will run me. I can add more in the rear later.
