Does Holland's lodging fill up in tulip season?

The only spot that should make a difference vis-a-vis tourists, Jerry, is Keukenhoff Gardens near Lisse/Leiden. That said, hotel rooms in NL can be tough (except Amsterdam) most of the time. Lived in Den Haag for 3 years between '98/'02 and there were times when colleagues from out of town had to take a room at Rotterdam or Amsterdam to get something decent/reasonably priced unless booked well in advance.
If it was me (and we'll be there in late April) I'd ditch the car, use Haarlem or Den Haag for a NL home base, and take the train/tram(had company car but almost always used train/tram wkends). Covered a lot of ground in NL and Belgium on business and days-off and would be pleased to offer suggestions for itinerary. Best to do that offline probably but in short, for 7 days in April, would suggest visiting Keukenhoff, Amsterdam, Haarlem, Den Haag, Delft, Antwerp and Brugges. If you're convinced a car's the way to go, I've other suggestions for out of the way spots.

Geoff, thank you for the reply. We first noted on the net that an occasional lodging was unavailable in late april then phoned a couple B&Bs in alkmaar area only to find them filled. Have since learned others seem to be available. We prefer to travel wo reservations tho r now seekg to book a B&B for 3 nights near alkmaar. We are set on a car, as our interest is more in outlying areas than cities, tho do want to catch transport into amsterdam, bruges & maybe leiden-pilgrim museum. We plan to drive circle around IJsselmeer 1 day & also see enkhuisen, lelystad & edam &/or volendam/marken. Plan to leave alkmaar on 3rd day, friday, so as to hit the Gardens & tulip drive, lisse to leiden, before weekend. Hope to find a budget B&B that night in zeeland. Sat want to see the storm dike museum & bruges & on to rural B&B. I very much APPRECIATE your offer to suggest some other places. Want visit Ardennes-only thots so far are bastogne memorial & folk museum nr Liege, then ParkVeluwe.