My temporary solution that became a permanent one was stacking wood 4x4's on the inside of the fenders. On my trailer 3 of them stacked were the perfect height to be just a tad higher than the fender, then I just cut each one off at an angle to make a decent ramp to drive over. I ran two lengths of 2x4's vertically on each side and screwed it into the 4x4 to hold them together, then ran a couple of bolts through the 4x4 and into the fenders to hold them in place. Having some sort of drive over fenders or ramps is a lot quicker and easier when loading and unloading versus having to remove fenders each time. On my 18' tandem axle trailer the weight distribution works out perfect if I drive the front tires over the fenders and pull the rears right up against the 4x4's.
The only downside to the drive over fender option is if you break something as it could be much harder to get loaded or unloaded. I've broken the steering (sheered all the bolts off the steering arm on the knuckle) and it was kind of a pain to get loaded as you need to be a little more precise to bet on the ramps, but even worse was breaking one front axle and being in 3wd. Got it loaded okay but had issues being backed off the trailer. When reversing you have to pull the front tires over the fenders/ramps and it would spin and slide the rear axle over to the side, finally had to pull it off the trailer with another truck. Overall my recommendation would be to have drive over fenders but also have the option to remove the fenders all together if needed.