I had two pneumatic tyres first with a plastic hub that suddenly deflated whilst reversing causing the wheel to jam,managed with the help other campers to get the van in the correct position on site.
Local caravan shop only had complete assy so I had to buy a alco with metal hub, this lasted about 1 year, before it to went bang as i was reversing over the curb onto my drive.Since then I have used the normal alco solid wheel, you can buy quite broad width solid tyre which i have no problem going over gravel.
The pneumatic tyre assy tends to be broader and heavier than the solid wheel assy, if you have the centre positioned jockey wheel assy make sure that you have enough width to lift the wheel clear of the road.