Bank holiday weekends behave the same way on a smaller scale. Even outside the main school Lincolnshire coast holidays, a bank holiday weekend pulls in extra demand because it gives everyone an extra day off without using annual leave, so these particular weekends fill up faster than an ordinary one either side of them.
On the budget side, self-catering works in your favour with a bigger group. Cooking most meals in the caravan rather than eating out as a party of eight or ten keeps costs sensible, and splitting the shopping and cooking between the adults spreads both the effort and the spend. A shared static caravan holiday, or two units booked close together, usually works out considerably more cost-effective than the equivalent number of hotel rooms plus regular restaurant bills.
Off-peak months help enormously too. School holidays and the height of summer are when demand is tightest, so a late booking in May, September or October usually has far more choice than the same search in late July. The weather isn't guaranteed either way, but a coastal or countryside break in early autumn can be genuinely pleasant, with quieter paths and shorter queues wherever you stop for lunch.
On-site facilities are worth checking properly rather than assuming. Look at what's actually included in your stay versus what costs extra, whether the pool, if there is one, is heated and what hours it runs, and whether there's anywhere on site to eat if you don't fancy cooking every night.
Finally, don't assume last-minute means limited facilities. A short break booked at short notice still comes with full access to whatever's on site, whether that's a pool, a clubhouse or coastal walking routes nearby. It simply means less choice over which specific unit you get, which for a quick, spontaneous trip is rarely the deciding factor anyway.
Cost works differently too. A self-catering caravan holiday means you control your food spend, cooking most meals in rather than eating out for every one, which suits a longer stay or a bigger family group where restaurant bills add up fast. A hotel bundles more into the room rate but gives you less choice over how you spend each day.