I have a real nice bike rack that fits a 2" receiver that holds 4 bikes, and always secured the rack and the bikes with cable locks to the holes in the hitch where the safety chains normally go.  At the cost of wheels for bikes these days, I think I'd also want to secure the front wheel and take off the seat.  But with our pod, such an arrangement isn't practical since the receiver is 1 1/2" and it would just be too heavy to safely use.  We'll just hose the bikes off and dry them before putting them inside to travel.  

 The receiver framework should be beefed up with welding another cross member to add structural support.

Another alternative is adding some stainless tie down points onto the rear of the Pod through the wood  framework. Then tie from those points to the bike rack to add support and prevent cyclic bouncing.

This thread has some ideas as well.

Or, looking at it from the point of view of the profession from which I recently retired, if your spare tire breaks off and kills someone, FR will be a major player in the court proceedings.  If you re-purpose the spare tire holder, it's your nickel all alone, so be sure to buy a very large umbrella policy.

That said, it's bouncy, bouncy on the back of the pod and the receiver hitch isn't rated for much more than the spare. I wouldn't want my bikes back there. My solution was a hitch rack - click the link in my sig.

Your search will find many opinions and options. Good luck!

fred