Mounting off of the iCreate is very similar to mounting off any lego chassis; that is, with the exception of the metal. If you look at the iCreate by itself, it is meant to be mounted off by metal (there's assortment of screw wholes there). However, if you feel you have mastered mounting off of it with the metal pieces, and are feeling adventurous, go ahead and mount off with legos. Legos, just like the metal pieces can be connected with screws onto the iCreate. It is generally easier with metal though due to the bend-ability of the metal.
When mounting, especially if elevating your mount on top of stilts or any piece raising the CBC significantly above the level of iCreate, make sure that you have screws in at least four spots. If you only mounted your robots in two spots it would be subject for the CBC or any other arm or attachment to fall of during testing or the actual competition. Also, as a note for beginners: the lower, the better. The lower and simpler you keep things, the easier it will be to fix any structural errors and the less likely you'll be to have any wobbly attachments. Finally, you want to make sure that all your screws and bolts are on tight! This may sound like a small thing, but if you don't make sure all your screws and bolts are tight and sturdy at the foundation, later parts can be unbalanced and have unsteady results. Don't use only your fingers for tightness, but use the Allen Wrenches and the regular wrench to tighten the pieces.
Especially when working with the iCreate, it may be temping to bend some of the metal pieces when connecting an attachment. Bending is fine, but you need to beware. If you are a school-affiliated team, you may want to consult your maintenance men/women or school custodian to see if they have any tools that bend metal precisely. The more precise the metal is bent, the less chance it has for bouncing as the bot moves and the cleaner the wholes will line up for any further attachments. Also keep in mind before bending, that after your team does bend it, the harder it is going to be to bend to its original shape. For that reason, bending should be done only when you're completely sure that you are going to use that design, and that you have measured the places it will need to be bent.
Unlike the lego chassis, drop testing or stair testing is not recommended for the iCreate. Instead, using two fingers, apply a medium to heavy pressure against each side of your mount, making sure that it doesn't move. If the iCreate mounting is not sufficiently sturdy, try either tightening any screws or bolts that may have become loose or try attaching additional pieces between the iCreate and the platform of the CBC. As said before, when more points are attached to something, the sturdier it will be.