Most people bolt them with the bolts passing all the way through the transom. Use stainless bolts and decent-sized washers to spread the load. When you drill through, you will need something to seal the exposed edges - take advice. Read the instructions, be methodical, and do a dry run before doing any drilling.
Be careful that the wheels do not foul the tubes when they are up/down/in transition. Also, bear in mind that in certain positions, the wheels may restrict the degree to which the outboard can turn. My wheels are on steel legs and are meant to be raised so that the wheels are above the transom. However, I find that for slow, tight manoeuvring and reversing it is best to let the wheels float rather than locking them in the up position.
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