What brand of bulbs are you using? e.g. In the past ive found the cheapo Ring/osram bulbs seem good value for money but dont last, especially with the jarring of harder suspension. I always use Phillips bulbs these days. I had Phillips VisionPlus H7/H1 bulbs in my last 1.6 16V dyna + for 4000 miles with no problems.
BTW, make sure you dont touch the quartz glass when putting the bulbs in. This causes hot spots on the glass, shortening their life. Easy to say ...took me a whole afternoon to change the dipped H7 bulbs on the dyna+ ....absolute swine with the air-con pipes on the drivers side!