I have made 1 like the 1st pic to sit on concrete, I didn't have heavy vintage bikes in it but it held a Moondog which was on the heavier side, an aluminum Giant cruiser, & 2 more box store bikes. The heavier you build it the stronger it is & use decking screws. Overkill planning vs bikes tipping over. May have to line them up front, rear, & front depending on wide bars etc. I did but 4 bikes so if you do 2 bikes you can space them accordingly based on your bed side widths