Start by thinking of fronted adverbial clauses to indicate that time has moved on.
E.g. Later that day, That afternoon, Just before sunset, After school, As the sky darkened.
Now, use a fronted adverbial clause to show that time has moved on to start your sentence. Don't forget to use a comma after the clause.
E.g. Later that day, Jelly wanted to visit Gran and tell her all about the project.
Think of some 'ing' verbs to describe Jelly's movement style.
E.g. rushing, dashing, hurrying, darting, hurtling, sprinting.
Assemble a bank of negative adjectives for the caravan.
E.g. dusty, rain-stained, corroded, rust-streaked, murky, dingy.
Build a complex sentence using powerful 'ing' verbs.
E.g. Racing to see Gran, Jelly saw her paint-peeled, algae covered caravan.
Now, think of alliterative pairs to negatively describe the caravan.
E.g. mouldy and mildew, worn-out and wobbly, dilapidated and dingy, cold and corroded, grey and grimy.
Use alliterative pairings to describe the caravan.
E.g. It was damp and dank. It was distressed and disbelieved. It was rusty and rickety but Gran loved it. She called it her Gran-a-van.