We have just acquired a Seascape Expedition double kayak. The boat weighs ~100 lbs. It's too long to fit on the kayak storage shelves I built in our garage for our single boats (in fact, it's too long to even fit in our two-car garage diagonally, without any cars in the garage!)

I would like to find a rack, similar to the Martin Creek rack (and other similar systems), that can accommodate such a heavy, wide and tall boat. The Martin Creek website says it's rack is designed for boats up to 90 lbs. I like the looks of the product here (http://www.suspenzkayakstorage.com/store/2035439/product/001) but know nothing about the company or this product, and I hate buying stuff online without a reference and recommendation.

What rack do you use to store your huge double kayak on the side of your house?

I would imagine that you could make some high brackets on the side of a house and use something like this pully system I use inside a garage. The double pullies can handle a heavy load easily and are easy to make. It would be cheaper and much stronger than the commercial ones you are looking at. From the looks of those J brackets, I would not trust them with 50 lb each on the short mounting bracket. A tremendous moment arm in that arrangement would tend to rip off the wall with 100 lb load.
http://www.krabach.info/kayak_hoist/hoist.html

For a boat that size, if you've got a yard, you should build a boat storage tube with a lockable door on the end. I've even considered sliding a kayak under the house in the crawl space.

I considered all sorts of hanging and rack schemes for storing two of my kayaks, but I didn't like the idea of having to fool around with lifting them and having them in the way of some of my activities in my shop. My solution was to build a multi-kayak storeage cart. They are stored on padded positions, on edge. The cart has castor wheels and is easy to shuttle around and even out of the shop when necessary. The whole thing was made from one sheet of 3/4" plywood--and a whole shop full of wood working equipment.